A mixture of 2,3,5- and 3,4,5-trimethylphenol is synthesized from the chlorination of isophorone as intermediates in the production of the pesticidal compounds 2,3,5- and 3,4,5-trimethylphenyl methylcarbamates. The reaction product mixture from the chlorination of isophorone contains the desired isomers of trimethylphenol as well as from about 5% to about 10% by weight of unreacted isophorone, and about 14% to about 23% by weight of by-products such as chlorotrimethylphenol, tars and high-boiling residue. The tars and high-boiling residue can be removed by distilling the mixture. However, the major remaining impurities, isophorone and chlorotrimethylphenol, cannot be satisfactorily removed in a conventional fractional distillation because the boiling point of chlorotrimethylphenol is very close to the boiling points of the trimethylphenol isomers and isophorone forms a maximum-boiling azeotrope with the trimethylphenol isomers that is about 5% by weight isophorone. As a result, it is not possible to obtain trimethylphenol by conventional fractional distillation of a purity greater than about 96% by weight that is acceptable for the production of 2,3,5- and 3,4,5-trimethylphenyl methylcarbamates.
U.S. Pat. Nos. 3,392,090 and 3,830,708 disclose the purification of phenolic compounds by azeotropic distillation with the formation of 2,6-dimethylphenol/glycol, acylic ketone/glycol and mixed hydrocarbon/glycol azeotropes. U.S. Pat. Nos. 3,827,974 and 3,331,755 disclose the purification of phenolic compounds by extractive distillation. None of these references, however, disclose the separation of alicyclic ketones or chlorotrimethylphenol from trimethylphenol by azeotropic distillation.